Direct-viewing color display storage device



P. P. DAMON Oct. l5, 1968 DIRECT-VIEWING COLOR DISPLAY STORAGE DEVICE 2 Sheets-Sheet l Filed Deo.

Phillip P. Dumon,

lNvENToR.

ATTORNEY,

Oct. l5, 1968 P. P. DAMON DIHECT-VIEWING COLOR DISPLAY STORAGE DEVICE Filed Dec. ll, 19554 Fig. 2.

209.52m @Ev-oom (Milliseconds) TIME Fig.

Time Milliseconds) fl f2 Phillip P. Damon, Time (Milliseconds) |NVENT0R,

ATTORNEY.

United States Patent 3,406,310 DIRECT-VIEWING COLOR DISPLAY STORAGE DEVICE Phillip P. Damon, Vista, Calif., assignor to Hughes Aircraft Company, `Culver City, Calif., a corporation of Delaware Filed Dec. 11, 1964, Ser. No. 417,706 11 Claims. (Cl. 315-12) ABSTRACT 0F THE DISCLOSURE YApparatus and method for displaying Vstored visual displays in different colors as a function of brightness or signal level which is achieved by applying increasingly negative potentials on the storage target backplate to progressively cut off lower brightness levels while shifting the output color of the viewing screen from one color to another.

The present invention relates to electronic storage devices and especially to direct-viewing storage tubes capable of providing presentations in color of given information. More particularly, the invention relates to methods and means for controllably displaying half-tone brightness levels in ditferent colors in a storage display tube.

One of the types of direct-viewing storage tubes to which the present invention relates is described in U.S. Patent 2,790,929 to E. E. Herman and G. F. Smith, and assigned to the instant assignee. This storage tube comprises a target assembly which includes a storage target and a viewing screen. Two electron guns are provided; one gun (hereinafter called the writing gun) causes the formation of a charge pattern on the storage target corresponding to the information to be presented, and the other gun (hereinafter called the ood or viewing gun) renders the charge pattern visible on the viewing screen. Information-representative signals are employed to modulate the intensity of the electron beam produced by the writing gun. The storage target is initially uniformly charged negatively. When the writing beam strikes the storage target, a less negative potential is produced at the point of impingement by the phenomenon of secondary emission. It should be understood that as used herein in describing the storage or charge pattern on the storage target, the term positive designates those portions which are less negatively charged than other portions of the target. The potentials on the storage target are always negative with respect to the potential of the flood gun cathode except when erasing. Thus by scanning the storage target, an overall charge pattern corresponding to the information to be presented is obtained. Thereafter this charge pattern controls the passage of flood electrons from the viewing gun to the viewing screen; flood electrons, properly collimated over the entire area of the storage target are only passed through areas of the storage target which are less negatively charged. It should be understood that the potentials capable of being stored range from a uniformly negative black value to a uniformly positive white value; at intermediate potentials only a portion of the ood electrons passes through the storage element to the viewing screen thereby producing intermediate or half-tone shades.

The present invention also pertains to direct-viewing half-tone storage tubes of the type described in U.S. Patent 3,086,139 to N. H. Lehrer, assigned to the instant assignee, loften referred to as a multimode storage tube because of the ability of this tube to present both stored and nonstored displays and to selectively erase portions of the stored display. In such a multimode storage tube, the phenomenon of bombardment induced conductivity is utilized to provide the storage mechanism. The bombard- 3,406,310 Patented Oct. 15, 1968 ICC ment induced conductivity storage target is responsive to the energy level of an electron beam impinging thereon whereby at one beam energy level the principal effect is secondary electron emission greater than unity. Such secondary emission permits the development of an electrostatic storage pattern corersponding to that described in the aforementioned patent to E. E. Herman and G. F. Smith. At a different beam energy level the principal effect is bombardment induced conductivity which permits the storage target to be charged in an opposite electrical sense so that charges previously stored by secondaryV emission, may be selectively erased by scanning the target with a beam at this second energy level. It is also possible, by utilizing an electron beam having an intermediate energy level, to cause some of the beam to pass through the storage target without having the portion of the beam which strikes the storage target appreciably alter the stored charge pattern or other potential conditions of the storage dielectric. Thus, the electron beam of such intermediate energy level can be used to establish the display of nonstored 4or live information simultaneously with the stored information. It will be understood that in both of the types of tubes described, display of stored information is achieved by the penetration of flood electrons through the storage target in accordance with the storage potentials thereon.

The desirability of providing such direct-viewing halftone storage tubes with a capability for displaying stored information in different colors will be readily apparent. Thus, for example, where such tubes are used for the display of navigational or target type information, it is often difficult to distinguish different light brightness levels in a black and white half-tone display of information. In direct-viewing storage tubes where in the display is established by impingement of the ood electrons on the viewing screen, it is possible to eliminate the display of low brightness level signals altogether simply by setting the potential level on the storage surface so that the flood beam is cut off for signals below some predetermined level and only the high brightness level signals are displayed. The disadvantage with such a proposal, however, is that one loses the low brightness level signal display while also having to operate with less than full brightness displays.

Although color display storage tubes have been previously proposed, I am not aware that any such tubes have been capable of directly converting half-tone level signals into displays of different colors as a function of signal strength without the use of extensive electron masking electrodes or grids and/ or `relatively complex color phosphor viewing screens. Thus, in U.S. Patent 2,818,524 to S. T. Smith and L. L. Vaut-Hall the viewing screen comprises an array of a multitude of discrete color phosphor dots and a storage target including one aperture in alignment with each pohsphor dot, with the sizes of these apertures being different and peculiar to phosphor dots of each color. C. D. Beintema in U.S. Patent 2,962,623 discloses another color display storage tube in which the color phosphor areas are arranged in a ring-dot configuration. The focus or spreading of the flood electrons as a function of charge image level causes their impingement upon either the dot phosphor or the dot plus the ring phosphor areas. While the present invention may be practiced in connection with such color storage tubes, it is by no means limited thereto and may be used to advantage with other types of color viewing screens as will be described in greater detail hereinafter.

It is therefore an object of the present invention to provide an improved direct-viewing half-tone storage tube capable of controllably presenting stored displays in different colors as a function of brightness or signal level.

Yet another object of the present invention is to provide an improved direct-viewing half-tone storage tube capable of controllably presenting in different colors what would otherwise be monochromatic brightness levels.

These and other objects and advantages of the invention are achieved by utilizing in an otherwise conventional half-tone direct view storage tube a viewing screen capable of selectively luminescing, in response to electron bombardment, in two or more primary colors. The viewing screen may comprise two or more superimposed phosphor layers each producing light of a different primary color, for example, and be of the type known as a penetration phosphor viewing screen which shifts color as a function of electron landing energy. In a typical embodiment, the penetration phosphor screen may include a green phosphor layer on which a red phosphor layer is superimposed.

The invention is based on the fact that areas of displayed information may be cut olf or extinguished by adjusting the relative potential between the ood electron source and the storage target. This may be achieved by applying an increasingly negative potential, for example, on the backing electro-de of the storage target from its normal voltage so that dilerent brightness level areas proceeding from low to high brightness areas will be progressively cut oft as the backing electrode becomes more negative. By shifting` the luminescence of the viewing screen from red to green at a time (Z1) 4after low brightness level areas are cut off by a negative-going waveform on the backing electrode, llow brightness levels may be :made to appear in red light, while intermediate and high brightness level areas may be made to appear in orange and green light, respectively. In the case of a penetration phosphor viewing screen the color shift is accomplished by changing the phosphor screen voltage at the time (t1) by which low brightness level areas have been cut off, for example. In this manner, half-tone brightness levels may be displayed in different colors.

The invention will be described in greater detail with reference to the drawings in which:

FIGURE 1 is a schematic diagram of a direct-viewing half-tone storage display tube device according to the present invention;

FIGURES 2 and 3 are diagrams of various pulse waveforms for use in explaining the operation of the present invention; and

FIGURE 4 is a graph in which color brightness levels are plotted against the time cycle of the backing electrode and viewing screen waveforms for explaining the operation of the present invention.

Referring now to the drawings a half-tone visual display cathode ray tube 2 of the type described in the aforementioned patent to Herman et al. or Lehrer is shown according to the present invention. The tube 2 comprises an evacuated envelope formed by a comparatively large cylindrical section 4 and a narrower neck portion 6 communicating therewith at one side thereof (hereinafter referred to as the neck or gun side). The side of the large cylindrical section 4 opposite the neck side comprises a faceplate 8 over the inner surface of which may be disposed a phosphor target or Viewing screen 1t) covered with a thin lm electrode 12 of metal, such as aluminum, for example. Alternatively, the phosphor viewing screen or target may be disposed on a transparent glass substrate member 9, as shown. The substrate member 9 may then -be secured by clamps or brackets or the like to the faceplate 8. The embodiment shown which includes the substrate member 9 is especially useful for phosphor layers which are formed by vapor deposition in vacuum. Thus, the substrate member 9 may be provided with the desired phosphor materials prior to assembly` in the tube 2 since it may be inconvenient to attempt to vapor-deposit the phosphor materials onto the faceplate 8 itself of the tube Z. Thereafter, the phosp'hor-coated substrate member 9 may be mounted in the tube 2 and adjacent the faceplate 8 as shown.

The phosphor viewing screen or target 10 may be of the penetration phosphor type and comprises a first layer 11 of phosphor material capable of emitting light primarily in the green region of the visible spectrum 'as a function of electron landing energy. Disposed over this green phosphor layer 11 is a second `layer 13 of phosphor material capable of emitting light primarily in the red region of the visible spectrum, likewise as a function of electron landing energy. Such viewing screen target structures are known in the art and further detailed description thereof is not deemed necessary herein except to note that in the typical red-green color phosphor structure described, the light output color is dependent upon the landing energy of electrons impinging on the target. Thus, landing energies of 8 or 1l kv., for example, will result in the production of red or green light, respectively. Such a color shift may be produced by switching the potential on the viewing screen itself.

Adjacent and coextensive with the viewing screen 10 is a storage target 14 as described in the aforementioned patents to Herman et al. or Lehrer. The storage target 14 may comprise a nickel mesh support, which may be electroformed, having disposed on one side thereof a thin layer or lm of magnesium uoride or cubic zinc sulfide, for example.

A collector grid 16 is disposed adjacent and coextensive with the storage target 14 and comprises a conductive screen which may be supported about its periphery by an annular ring (not shown). The function of the grid 16 is to collect secondary electrons emitted from the storage target 14.

A ood gun 30 is disposed on the longitudinal axis of the tube 2. The flood gun 30 comprises a cathode 32 and an intensity electrode member 34 which enclose's the cathode 32 except for a small aperture in the end of the electrode member 34 and in alignment with the central portion of the cathode 32. An annular electrode member 38 is disposed adjacent the intensity electrode 34 and coaxially with respect to the longitudinal axis of the tube 2 which also passes through the center of the aperture 36 in the intensity electrode member 34.

The neck portion 6 of the tube 2 houses a first electron gun 40 which may be of conventional construction for providing an electron beam of elemental cross-section area. The gun 40 comprises a cathode 42, an intensity electrode grid 44, and a cylindrical beam-forming section 46. Horizontal deflecting plates 48 and vertical detlecting plates 48 for controlling the deflection of the electron beam generated -by the electron gun 40 are also provided. Also shown as housed in the neck portion 6 of the tube 2 is a second electron gun 50 of conventional construction for providing a second electron beam of elemental crosssectional area. The gun 50 comprises a cathode 52, an intensity electrode grid 54 and a cylindrical beam-forming section 56. Horizontal and vertical deliecting plates 58 and 58 respectively are likewise provided. While electrostatic deflection means are shown, the electron beam from the two guns may be magnetically focused and deflected, in which case separate neck portions may be desirable. I

It is possible according to the present invention to utilize only one electron gun for forming an electron beam of elemental cross-sectional area. Thus, where only storage and nonselective erasure functions are desired as in the storage tube described in the aforementioned patent to Herman et al., a single writing gun need be provided. Likewise only one writing gun may -be employed in the aforementioned bombardment induced conductivity tube of the Lehrer patent, in which case time-sharing of the three functions of storing, erasing and presenting live or nonstored information (hereinafter calledA writingthrough) is necessary. Because it is desirable to provide a tube having the capability of presenting simultaneously stored and nonstored information, it is preferred to provide two electron guns as shown, one for writing stored information and the second for presenting nonstored information and for erasing stored information. Hereinafter the first electron gun 40 will be referred to as the storage gun while the second electron gun 50 will be referred to as the live gun, and it will be understood that the second gun may be switched to provide live presentations and erasure on a time-sharing basis.

Collimation of the flood gun electrons over the storage target 14 is achieved by applying proper potentials to the collimating electrodes or conductive layers 49, 49' and 49 which are coated over the interior surfaces of the tube as shown.

The electron beams produced by the two electron guns 40 and S0 are caused to scan the storage target 14 and/ or Viewing screen by means of horizontal and vertical deflection voltages generated by horizontal and vertical deflection generators (not shown). The cathode 52 of the Llive information gun 50 may be maintained at a potential of the order of 4.5 kv. negative with respect to ground. The electron beam from this gun has an energy level at which the rate of charge of the storage surface by secondary electron emission is counter-balanced by the rate of discharge by bombardment induced conductivity resulting in a zero net change in charge on the storage surface when the potential of the storage target is substantially zero. The intensity grid 54 of the live gun 50 may be maintained at a quiescent potential of 'about 75 volts negative with respect to the potential of the cathode 52. The intensity of the electron beam from the live gun 50 may be modulated in accordance with video or other type of information signals such as radar information signals, for example.

The cathode 42 of the storage gun 40 may be maintained at a potential of about 2.5 kv. negative with respect to ground. The intensity lgrid 44 of the storage gun 40 may be main-tained at a quiescent potential of about 75 volts negative with respect to the cathode 42. The intensity of the electron beam from the gun 40 may also be modulated in accordance with video or radar information signals which it is desired to display for continued periods of time.

The cathode 32 of the flood gun 30 is referenced to ground. The intensity electrode 34 and the annular electrode 38 may be maintained at potentials of the order of and plus l0() volts, respectively, with respect to ground.

The storage target characteristics is such that with a beam energy from a gun Whose potential is about 1.0 kv. negative, positive charging (which means charging the potential of the storage surface) is at a maximum and is almost entirely due to the secondary electron emission phenomenon, any charging due to bombardment induced conductivity being negligible and rather completely overridden by the secondary emission effect. Thus with a primary beam energy of from 1 to 4.5 kv. the storage target is charged positively by the secondary emission phenomenon.

At about 4.5 kv. secondary emission still occurs but bombardment induced conductivity effects will have increased to the point where both phenomena charge the storage surface in equal but opposite electrical senses, hence the storage surface potential will be relatively undisturbed when the storage target is bombarded by a beam of about 4.5 kv. With beam energies greater than about 4.5 kv. the bombardment induced conductivity effect increases further and rather completely overrides the secondary emission effect which continues to diminish. The net charging effect on the storage surface hence is to drive it negatively to an equilibrium potential by the bombardment induced 4conductivity effect.

It will thus be appreciated that the storage target utilizes two phenomena to produce charging effects in opposite electrical senses which effects may be balanced so as to result in no net charging effect in either electrical sense. This is possible because there is a continuous range of electron beam energy levels where both secondary electron emission and bombardment induced conductivity occur and because at different portions of this range either of these phenomena can be made dominant or the two phenomena can be balanced. The capability of balancing these two phenomena is of significance where it is desired to provide a storage target which can be written-through to present direct or live information without altering the potentials on the storage target.

Operation of the storage tube may be accomplished as follows. A potential of 'about 9 volts negative relative to ground is applied to the nickel mesh support or backing electrode of the storage target 14. lf we assume that the storage dielectric is initially at the same potential as the storage mesh, then, as a result of the application of the -9 volt potential to the storage mesh or backing electrode, the storage dielectric will be carried by capacitive coupling to -9 volts. Under these circumstances liood electrons from the gun 30 will be prevented from passing through the openings in the storage target 14 (because of the 9 volt negative potential on the storage dielectric). Hence the ood or viewing electrons cannot reach the viewing screen and excite it into luminescence. This is the initial dark condition of the tube.

To store and display information, the storage target 14 is scanned by an electron beam of elemental crosssectional area having an energy level relative to the storage surface of about 2.5 kv. or less. As indicated previously, this beam may be generated by means of the electron gun 40 whose cathode 42 is maintained at a potential of about 2.5 kv. negative will respect to ground.

Areas of the storage target 14 impinged by the beam from the electron gun 40 in accordance with the information to be displayed are charged positively due to the emission of electrons therefrom which are collected primarily by the collector grid 16 which may be maintained at a potential of volts positive with respect to -ground in order to accomplish this function. Viewing or ood electrons from the flood gun 30 may then pass through the storage target 14 at these areas of positive potential and are then accelerated to impinge upon the phosphor viewing screen 10 by means of a potential of 'about 8,000 volts positive with respect to ground which may be maintained on the aluminum film 12 of the viewing screen. At this viewing screen potential and in this manner the formation is displayed as red light and the display may be maintained and viewed as long 'as desired.

Nonstored or live information may also be simultaneously displayed by scanning the viewing screen 10 with an electroni beam from the electron gun 50. As explained previously, in order to write or display live information, a beam having a energy level of about 4.5 kv. is required. Such a beam will pass through the storage target 14 without appreciably altering the potential of either positively or negatively charge portions.

The live gun may be caused to selectively erase stored potentials on the storage target 14 by operating the gun at its normal energy level of 6.0 kv. The storage target 14 is thus scanned with a beam having such an energy level in accordance with signals representing the information to be erased. The impingement of a beam of 6.0 kv. energy on portions of the storage target results in these portions being charged negatively to about the potentials of the nickel support mesh 4 (-9 volts) by means of the phenomenon of bombardment induced conductivity, as explained previously.

It will thus be understood that oo-d electrons for creating visible stored displays penetrate the storage target in accordance with the potentials thereon and that the storage potentials control the intensity of the flood beam so as to create half-tone displays ranging in brightness from 0-l00%. The present invention permits the display of various brightness levels in different colors.

With reference to FIGURES 2, 3 and 4 it will be appreciated that during the time tl-to the viewing screen target 10 is operated at a viewing screen potential of about 8.0 kv. so as to cause the viewing screen to luminesce in red light. Likewise during this same time period a negative-going Waveform potential is applied to the backing electrode of the storage target i4. Hence, low brightness level displays such as represented by Curve A will have diminished and will no longer be Visible by the time, t1. High brightness levels as represented by Curve B, however will continue to luminesce and will not have diminished until an additional period of time, t2-t0, has elapsed. The cutting-olf of first the lower brightness and then the higher brightness areas of the display may be achieved by progressively changing the potential on the backing electrode from just slightly negative from its normal voltage. Alternatively, the relative potential between the flood gun cathode and the backing electrode of the storage target may be controlled to cut off fiood electrons by holding the potential on the backing electrode at a fixed value and changing the potential on the cathode of the flood gun. In either event, flood electrons are gradually prevented from penetrating through portions of the storage target so that high brightness areas will not be cut off until the backing electrode reaches a maximum cut-off potential relative to the flood gun cathode. Depending upon the phosphor efficiency and the eifect desired, tl-ro may be about 4 milliseconds and t2-t0 may be about 10I milliseconds. These conditions may be realized by applying a negative-going sawtooth wave or pulse form (W) to the backing electrode by means of the waveform generator 60. By switching the viewing screen potential to the voltage at which the viewing screen luminesces to produce green light, which potential may be about 1l kv., and synchronizing the viewing screen potential switch with the backing electrode pulse waveform the potential shift on the viewing screen may be made to occur at time t1. Hence, the color Iof the display will shift from red to green light. Since by this time (t1) low brightness areas are cut off by the negative-going pulse on the backing electrode of the storage target, only the high brightness level areas such as represented by Curve B in FIGURE 4 will be displayed predominantly in green light. Intermediate brightness level areas such as represented by Curve C in FIGURE 4 `will be on during the red period and for a slight portion of the green period, and the integrated effect on the eye will be an orange display. Increasingly higher brightness areas will appear as yellow and then green. The shifting of the color produced by the viewing screen 10 is achieved by means of wave generator 62 which applies a pulse having the form shown in solid lines (Y) in FIGURE 3. In this manner the level of brightness areas is indicated by different colors in the display. In order to avoid objectionable icker to the human eye, the synchronized voltage waveforms applied to the backing electrode of the storage target and to the viewing screen should have a repetition rate greater than the icker frequency of the human eye.

It will be understood that many variations in the technique just described are possible and will occur to those skilled in the art. Thus, while an abrupt or step-like switch or shift from one viewing screen potential to a second has been described, a gradual shift may be desired in some instances and provided by means of a Waveform such as represented by dashed lines (Z) in FIGURE 3. Likewise, different waveform potentials may be applied to the backing electrode of the storage target for other desired special effects. Thus, the brightness displays in one primary color maybe accentuated or increased by applying a waveform to the backing electrode of the storage target as represented by the dashed lines (X) in FIGURE 2. It will be clear, therefore, that it is within the scope of the practice of the present invention to utilize variously shaped Waveforms, both linear and nonlinear, to obtain different effects such as rapid or gradual change from one color to another or the accentuation of a particular color.

While the practice of the invention has been described in connection with an initial time period in which displays appear in red, it will be understood that one may start with displays in any color. Because of the known greater efficiency of green phosphore it may be preferable to follow a schedule such as described herein unless one makes special previsions to have the green displays effectively overridden or superseded by displays in other colors where the phosphor efficiencies are less than those for green phosphors. Furthermore, while the practice of the invention has been described with respect tothe use of penetration phosphor viewing screen structures, other viewing screen arrangements may be used providing they have a capability of luminescing in different colors under the control of or in response to an electrical potential. The means for causing the viewing screen to luminesce in different primary colors may be provided either internally ywithin the tube or externally thereof. Thus, electrically switchable or controllable col-or lters may be disposed in front of a black-and-white viewing screen structure so that the different color filters may be switched in accordance with the desired color sequence.

While, as just indicated, other arrangements may be used to provide color displays than those described in detail herein, the employment of a penetration phosphor target has certain advantages. Thus there are no alignment problems as with other types of color cathode ray tubes which employ shadow mask and dot phosphor arrangements. Furthermore, since the penetration phosphor is formed by laying one phosphor coating over another, there are no diicult phosphor fabrication problems as involved in color cathode ray tubes employing dot phosphor arrangements.

The operation of a direct viewing storage tube in a manner to permit the display of live information (in contrast to stored displays) has generally been described previously. In connection with the practice of the instant invention, the live or written-through displays can be made t-o appear as either green or blue. In a typical ernbodiment, a penetration-type phosphor target may ernploy three phosphor layers (i.e., red, green and blue) with the blue phosphor layer requiring an electron landing energy of 15 ikv. Thus, with an 8 kv. potential on the viewing screen, the apparent electron landing energy of the write-through beam will be about 12.5 kv. (since the write-through beam has an energy -of 4.5 kv.). Hence, while the stored displays will be appearing in red light, for example, the Write-through will appear as green. When the viewing screen potential is shifted to 11 kv., the apparent electron landing energy of the write-through beam will be 15.5 kv. Hence the live information will appear as blue. It is, of course, possible to employ a penetration-type phosphor target having only two phosphor layers and let the write-through information always appear as pure green. This latter arrangement has some disadvantages since color discrimination between live and stored information may be lost during some period.

There thus has been described a new and improved direct-viewing half-tone storage tube in which displays in different colors are provided indicative of different brightness levels. The practice of the invention is particularly suitable for use with cathode ray storage tubes of the multimode storage type since stored picture brightness levels may be displayed lor indicated in color without affecting or being affected by the high energy writing beam employed for establishing nonstored visual displays. While the invention has been described with particular reference to multimode storage tubes of the type described in the aforementioned patent to Lehrer, the practice of the invention is by no means limited thereto but may be practiced with any direct-viewing storage display tube, particularly of the type described in the aforementioned patent to Herman et al. It is also possible to operate the storage tube so that only black-and-white (monochromatic half-tone color) and not polychromatic color half-tone displays are produced. To this end, the backing electrode and the viewing screen may be Set at static potentials 'with the viewing screen voltage determining the color in which it is desired to `observe the half-tones.

What is claimed is:

1. In a cathode ray storage tube of the type having viewing screen means capable of effectively luminescing in different colors in response to the impingement of electrons thereon and a storage target for controlling the passage of flood electrons to said viewing screen, the method of displaying different brightness levels in different colors on said viewing screen means comprising: controlling the passage of flood electrons through said storage target as a function of brightness level while causing said viewing screen means to effectively luminesce in different colors as a function of time.

2. In a cathode ray storage tube of the type having viewing screen means capable of effectively luminescing in different colors in response to the impingement of electrons thereon and a storage target for controlling the passage of flood electrons to said viewing screen, the method of displaying different brightness levels in different colors on said viewing screen means comprising: limiting the passage of flood electrons representing predetermined brightness levels through said storage target to one time period while causing said viewing screen means to effectively luminesce in one of said colors during said time period, and permitting flood electrons representing brightness levels different from said predetermined brightness levels to pass through said storage target during a different time period while causing said viewing screen to effectively luminesce in another of said colors.

3. In a cathode ray storage tube of the type having viewing screen means capable of effectively luminescing in different colors in response to the impingement of electrons thereon and a storage target for controlling the passage of flood electrons to said viewing screen, the method of displaying different brightness levels in different colors on said viewing screen means comprising: limiting the passage of flood electrons representing brightness levels below a predetermined level through said storage target to a first time period while causing said viewing screen means to effectively luminesce in one of said colors during said first time period, and permitting flood electrons representing brightness levels higher than said predetermined level to pass through said storage target during a succeeding time period while causing said viewing screen to effectively luminesce in another of said colors.

4. In combination, a cathode ray storage tube comprising: viewing screen means capable of effectively luminescing in different colors in response to the impingement of flood electrons thereon, a storage target for controlling the passage of flood electrons therethrough to said viewing screen in accordance with an electrostatic charge pattern established on said storage target, means for scanning said storage target with an electron beam to establish said electrostatic charge pattern thereon, means for flooding said storage target with flood electrons, means for applying potentials to said storage target for progressively cutting off the passage of flood electrons therethrough during a predetermined time period, and means for applying potentials to said viewing screen means to cause said Viewing screen means to effectively luminesce in different colors during said predetermined time period.

5. In combination, a cathode ray storage tube comprising: Viewing screen means capable of effectively luminescing in different colors in response to the impingement of flood electrons thereon, a storage target for controlling the passage of flood electrons therethrough to said viewing screen in accordance with an electrostatic charge pattern established on said storage target, means for scanning said storage target with an electron beam to estabish said electrostatic charge pattern thereon, means for flooding said storage target with flood electrons, means for applying potentials to said means for flooding said storage target with electrons to progressively cut off the passage of flood electrons therethrough during a predetermined time period, and means for applying potentials to said viewing screen means to cause said viewing screen means to effectively luminesce in different colors during said predetermined time period.

6. In combination, a cathode ray storage tube comprising: a viewing screen capable of luminescing in different colors in response to potentials applied to said viewing screen and to the impingement of flood electrons thereon, a storage target for controlling the passage of flood electrons therethrough to said viewing screen in accordance with an electrostatic charge pattern established on said storage target, means for scanning said storage target with an electron beam to establish said electrostatic charge pattern thereon, means for flooding said storage target with flood electrons, means'for applying increasingly negative potentials to said storage target whereby to cut off the passage through said storage target of flood electrons with flood electrons representing the highest brightness signal levels being cut off last, and means for applying potentials to said viewing screen to effect the luminescence thereof in successively different colors.

7. In combination, a cathode ray storage tube comprising: a viewing screen having at least two phosphor layers with one superimposed over another and each capable of luminescing in a different color in response to potentials applied to said viewing screen and to the impingement of flood electrons thereon, a storage target for controlling the passage of flood electrons therethrough to said viewing screen in accordance with an electrostatic charge pattern established on said storage target, means for scanning said storage target with an electron beam to establish said electrostatic charge pattern thereon, means for flooding said storage target with flood electrons, means for applying potentials to said storage target for controlling the passage of said flood electrons therethrough as a function of brightness level, and means for applying potentials to said viewing screen to effect the luminescence thereof in different colors while applying said potentials to said storage target.

8. In combination, a cathode ray storage tube comprising: a viewing screen having at least two phosphor layers with one superimposed over another and each capable of luminescing in a different color in response to potentials applied to said viewing screen and to the impingement of flood electrons thereon, a storage target for controlling the passage of flood electrons therethrough to said viewing screen in accordance with an electrostatic charge pattern established on said storage target, means for scanning said storage target with an electron beam to establish said electrostatic charge pattern thereon, means for flooding said storage target with flood electrons, means for applying potentials to said storage target for progressively cutting off the passage of said llood electrons therethrough during a predetermined time period, and means for applying potentials to said viewing screen to effect the luminescence thereof in different colors while applying said potentials to said storage target.

9. In combination, a cathode ray storage tube comprising: a viewing screen having at least two phosphor layers with one superimposed over another and each capable of luminescing in a different color in response to potentials applied to said viewing screen and to the impingement of flood electrons thereon, a storage target for controlling the passage of ood electrons therethrough to said viewing screen in accordance with an electrostatic charge pattern established on said storage target, means for scanning said storage target with an electron beam to establish said electrostatic charge pattern thereon, means for flooding said storage target with flood electrons, means for applying increasingly negative potentials to said storage target for progressively cutting off the passage of said flood electrons therethrough, and means for applying potentials to said viewing screen to effect the luminescence thereof in different colors while applying said increasingly negative potentials to said storage target.

10. In combination, a cathode ray storage tube comprising: a viewing screen having at least two phosphor layers with one superimposed over another and each capable of luminescing in a different color in response to potentials applied to said viewing screen and to the impingement of flood electrons thereon, a storage target for controlling the passage of liood electrons therethrough to said viewing screen in accordance with an electrostatic charge pattern established on said storage target, means for scanning said storage target with an electron beam to establish said electrostatic charge pattern thereon, means for ooding said storage target with ood electrons, means for applying increasingly negative potentials to said storage target whereby the passage of flood electrons representing brightness signals below a predetermined level through said storage target is cut olf by the end of a rst time period and for applying further increasingly negative potentials to said storage target during a second time period whereby the passage of flood electrons representing brightness signals higher thanV said predetermined level is cut oi by the end of said second time period, and means for applying potentials to said viewing screen to effect the luminescence thereof in a different color during each of said time periods.

11. In combination, a cathode ray storage tube com-V prising: a viewing screen having at least two phosphor layers with one superimposed over another and each capable of luminescing in a different color in response to potentials applied to said viewing screen and to the irnpingernent of ood electrons thereon, a storage target for controlling the passage of flood electrons therethrough to said viewing screen in accordance with an electrostatic charge pattern established on said storage target, means for scanning said storage target with an electron beam to establish said electrostatic charge pattern thereon, means for ooding said storage target with ood electrons, means for applying increasingly negative potentials to said storage target for progressively cutting off the passage of said -flood electrons representing brightness signals below a predetermined level during a iirst time period and for applying further increasingly negative potentials to said storage target during a second time period for progressively cutting oi the passage of ood electrons therethrough representing a higher signal brightness than said predetermined level, and means for applying a first potential to said viewing screen during said rst time period and a different potential during said second time period whereby said viewing screen is caused to 1un1inesce in one of said colors during said rst time period and a different color in said second time period.

References Cited UNITED STATES PATENTS 2,440,301 4/ 1948 Sharpe 315-22 2,446,248 8/ 1948 Shrader 250-164 2,818,524 12/1957 Smith et al. 315-12 3,086,139 4/1963 Lehrer 315-12 RODNEY D. BENNETT, Primary Examiner. JOHN W. CALDWELL, Examiner.

J. P. MORRIS, Assistant Examiner. 

